Direct recording method and direct recording apparatus

Abstract: In a direct recording method, the toner supplied on a toner carrier (1) contains at least fixing resin and magnetic grains, and has an apparent density of 0.5 g/cc or more and an angle of repose of 45° or less. The magnetic flux density on the toner carrying member (1) is 0.06 T or more. A doctor blade (5) located opposite the toner carrying member (1) is used to restrain the thickness of toner layer formed on the toner carrying member (1) to 5 to 100 µm. When recording on a recording body (4), the image density is improved and fogging is eliminated.

Description: Field of the Invention The present invention relates to a direct recording method wherein a recording electrode is kept in non-contact with a recording medium such as paper, and toner images are formed by toner jumping out from a toner carrying member directly onto the recording medium, and to a direct recording apparatus. Prior Art Conventionally, an electrophotographic device has generally been used as a device for forming an image such as documents or figures on a recording medium. However, since in electrophotographic devices a means for forming latent images on the surface of an image carrying member and a means for developing the images to be formed separately are required, the structure tends to be complex and large. A direct recording method has thus been proposed wherein a recording electrode and a background electrode are located opposite each other on a toner carrying member, a recording medium such as paper is transferred between the recording and background electrodes, a voltage corresponding to an image signal is then applied between the recording and background electrodes to generate a static electricity force, and in response to the voltage applied, the magnetic toner is blown off from the toner carrying member and onto the recording medium. Configuration for various direct recording methods have been proposed. Among them is a method of using a recording electrode with a plurality of conductors disposed like a matrix, and simultaneously applying a voltage to each conductor to cause magnetic toner retained on a magnet roll to jump out from the meshes of the recording electrode using static electricity and to selectively adhere to the surface of a recording medium (WO90/14959 and WO90/14960, the latter disclosing the features included in the first part of each of claims 1 and 2). Since this direct recording method uses a specific recording electrode, it can provide high quality images. In this direct recording method, when the toner jumps out from the toner carrying member onto the recording medium, it passes through many small holes in the matrix-like recording electrode. Therefore, there is a disadvantage in this method that when the toner jumps out from the toner carrying member onto the recording medium, it contacts the recording electrode and is difficult to become smoothly attached to the recording medium, often resulting in bleeding images or splashing toner. In addition, since the toner attracted on the toner carrying member cannot be stably retained, it is difficult to cause the toner accurately to jump onto the recording medium in response to the voltage applied to the recording electrode. Object of the Invention Therefore, it is the object of this invention to allow the toner to flow smoothly, to reduce the thickness of the toner layer formed onto the toner carrying member. and to enable the toner carrying member to retain toner properly, thereby improving image density and eliminating fogging. In accordance with the invention, this object is achieved by the method characterised in claim 1 and the apparatus characterised in claim 2. In a preferred embodiment, a doctor blade located opposite the toner carrying member is used to regulate the thickness of the toner layer formed on the toner carrying member to 5 to 100 µm. Preferably, a fluidity-improvement agent represented by an inorganic fine powder such as SiO 2 , Al 2 O 3 , or TiO 2 , or metallic salt of stearic acid such as zinc stearate or calcium stearate is added to the outer surface of the toner. The surface of the toner carrying member has a magnetic flux density of 0.06 T or more in order to retain the toner properly so as to prevent the image density from being reduced and the visibility of images from being degraded due to splashing. The thickness of the toner layer formed on the toner carrying member is preferably regulated to 5 to 100 µm because otherwise, many toner particles will jump out from the toner carrying member onto the recording medium and easily contact the small holes in the recording electrode to make high quality images difficult to obtain. The toner has an apparent density of 0.5 g/cm 3 or more and an angle of repose of 45° or less in order to have better fluidity, so that it can jump out properly and smoothly pass from the toner carrying member through the holes of the recording electrode onto the recording medium, thereby providing high quality images. Examples of materials for the magnetic toner used for this invention are listed below. The fixing resin is set as appropriate depending upon the fixing method (see US-A-4,433,042, for example). For example, styrene-acrylic copolymer, styrene-butadiene copolymer, polyester resin, epoxy resin and mixed resins thereof are appropriate for a heat roll fixing method, An alloy or a compound such as ferrite or magnetite containing a ferromagnetic element such as iron, cobalt or nickel can be used as the magnetic powder, and these particles should preferably have an avenge particle size of 0.1 to 3 µm so as to be contained in the toner particles. The magnetic powder should preferably has a coercive force i Hc of 40 to 400 A/cm. A range of 10 to 60 wt.% is appropriate for the content of magnetic powder with respect to 100 wt.% of toner. If the content of magnetic powder is smaller than 10 wt.%, the saturation magnetisation will be reduced, while if it is above 60 wt.%, the volume resistivity of the toner will be reduced due to its own conductivity, and the fixing property will also be degraded. Therefore, the preferable content is 20 to 40 wt.%. A charge control agent can be added to the toner, and in this case, a known dye or pigment may be used. For example, a dye including a nigrosine dye having positive frictional electrification or a metal-containing azoic dye having negative frictional electrification are possible. The content of this charge control agent is preferably set within a range of 0.1 to 5 wt.% so as to obtain the above charge amount. To improve the fluidity of the toner particles, inorganic fine particles such as silica (SiO 2 ), aluminia (Al 2 O 3 ), or titanium oxide (TiO 2 ) or metallic salts of stearic acid such as zinc stearate or calcium stearate are preferably added to the surface of the toner particles. The added amount should be 0.1 to 3 parts by weight relative to 100 parts by weight of toner particles. If the content is less than 0.1 part by weight, the desired improved fluidity cannot be achieved, while if it is above 3 parts by weight, the particles will have too high a charging capability. To perform this addition, for example, the toner particles and an additive are simply fed into a publicly known dry mixer and then agitated for a specified period of time. In the above direct recording method, since the toner retained on the toner carrying member contains at least fixing a resin and a magnetic powder and has an apparent density of 0.5 g/cm 3 or more and an angle of repose of 45° or less, as well as a good fluidity, it smoothly passes the small holes in the recording electrode without degrading the image quality. In addition, a value of 0.06 T or more for the intensity of developing pole (the magnetic flux density on the toner carrying member) allows the toner to be retained properly and prevents instably retained toner from jumping out in excess toward the recording medium, or from contacting the edge of the hole in the recording electrode. Furthermore, if the doctor blade is located opposite the toner carrying member to regulate the thickness of the toner layer formed on the toner carrying member to 5 to 100 µm, no excess toner is caused to jump out toward the recording medium, and uniform electrostatic force is applied to the toner to cause it to jump out onto the recording medium, thereby improving the image quality. Brief Description of the Drawing Figure 1 is a schematic view of a device to which a direct recording method according to this invention is applicable. Detailed Description of Embodiment A direct recording method according to this invention is implemented by a direct recording device shown in Figure 1. In this direct recording device, a background electrode 2 is located opposite a toner carrying member 1, and a matrix-like recording electrode 3 is located between the toner carrying member 1 and the background electrode 2. This device allows a voltage corresponding to images to be recorded to be applied to the recording electrode 3, and also allows a recording medium 4 such as paper to be transferred between the recording electrode 3 and the background electrode 2 to receive the toner from the toner carrying member 1. A doctor blade 5 made from ferromagnetic material such iron or steel is provided opposite the toner carrying member 1 to regulate the thickness of the toner layer formed on a sleeve 1a to a small value. The sleeve 1a is made from non magnetic and electrically conductive material such as austenitic stainless steel or aluminium alloy. The toner carrying member 1 comprises a roll-like permanent magnet member 1b with a plurality of magnetic poles (four in Figure 1) on its surface inside of the sleeve 1a with an outside diameter of 32 mm manufactured by SUS 304. A DC voltage source is connected between the sleeve 1a and the background electrode 2. Magnetic toner is supplied onto the sleeve 1a, and the relative rotation of the sleeve 1a and the magnet member 1b is used to transfer the magnetic toner to the opposite side where the recording electrode 3 is located. The toner used in the above direct recording device contains a fixing resin and a magnetic powder, and is added with a fluidity improvement agent. To provide the fixing resin, 60 to 80 wt.% of polyester resin and 20 to 40 wt.% of magnetic powder were dry-mixed, heated, and kneaded, cooled and solidified, and finally crushed. 0 to 1.0 parts by weight of SiO 2 (H2000 manufactured by Wacker Inc.) were added to the 100 parts by weight of crushed toner particles as a fluidity improving agent, and then mixed and classified to prepare magnetic toner with a volume average particle size of 7 µm, triboelectric charge of -50 µC/g, saturated magnetisation of 0.02 to 0.025 A/gm (20 to 25 emu/g), and a coercive force of 80 A/cm. This magnetic toner was used for the direct recording device. As shown in Table 1, the apparent density of this embodiment is 0.5 to 0.7 g/cm 3 while that of a comparative example was 0.35 to 0.45 g/cm 3 , and the angle of repose of this embodiment is 38 to 45° while that of the comparative example is 48 to 55°. The triboelectric charge was measured by a blow off triboelectric charge measuring device (TB-200 type manufactured by Toshiba Chemical Inc.), and the magnetic toner and a ferrite carrier (Hitachi Metals KBN-100) were used to prepare a developer with a toner concentration of 5 wt.%. The magnetic characteristic of the magnetic toner was measured by using a vibration sample magnetometer (VSM-3 type manufactured by Toei Kogyo Inc.) applying a magnetic field of 800 kA/m maximum. The particle size of the toner was measured by a Coulter counter model T-11 (manufactured by Coulter Electronics Inc.). To enable recording, the direct recording device was arranged as follows. A large number of holes were provided in the recording electrode 3 to allow the toner to pass through. The diameter of each hole was set to 0.2 mm, the gap between the recording electrode 3 and the sleeve 1a was set to 50 µm, and the gap between the recording electrode 3 and the background electrode 2 was set to 0.5 mm. The magnet member 1b in the toner carrying member was fixed, the sleeve 1a was rotated at 150 rpm, the doctor gap was set to 0.1 mm, and plain paper was passed between the background electrode 2 and the recording electrode 3 at a speed of 50 mm/sec. A voltage of 1,500 V was applied between the sleeve 1a and the background electrode 2, and a recording voltage of -300 V was applied to the recording electrode 3. The magnetic flux density on the sleeve at a magnetic pole S 1 opposite the doctor blade 5 was set to 0.07 T while the magnetic flux density on the sleeve corresponding to magnetic poles S 2 and N 2 was set to 0.06 T. Toner images were formed on the surface of the paper. Heat roll fixation was then performed at a fixing temperature of 180 °C, a fixing pressure (line pressure) of 1 kg/cm and a nip width of 4.0 mm. The toner was used in the direct recording device set as described above to obtain images. Table 1 shows the results of evaluation. Comparative Examples Embodiments of the Invention 1 2 1 2 3 4 Magnetic powder (wt.%) 30 30 30 25 20 35 SiO 2 (parts by weight) 0 0.3 0.6 0.7 0.7 1.0 Apparent density (g/cm 3 ) 0.35 0.45 0.5 0.65 0.6 0.7 Angle of repose (°) 55 48 45 43 40 38 Magnetic flux density of the developing pole N (T) 0.05 0.09 0.09 0.09 0.07 0.07 Image density 0.7 0.9 1.3 1.25 1.41 1.40 Fogging Yes Yes No No No No As is apparent from Table 1, the image obtained by this embodiment is preferable because it has an image density of 1.25 or more, no fogging, and good quality. In the comparative example, neither image density nor fogging characteristics were satisfactory. In the direct recording method according to this invention, since the toner supplied on the toner carrier has a good fluidity represented by an apparent density of 0,5 g/cm 3 or more and an angle of repose of 45° or less, it smoothly passes the small holes in the recording electrode to provide high quality images. In addition, the magnetic flux density of 0.06 T or more on the toner carrying member allows the toner to be retained properly and prevents instably retained toner from jumping out in excess toward the recording medium. Since the doctor blade located opposite the toner carrying member serves to regulate the thickness of toner layer formed on the toner carrying member to 5 to 100 µm, no excess toner jumps out toward the recording medium, and uniform electrostatic force is applied to the toner, thereby improving the image quality.

Claims: A direct recording method wherein a background electrode (2) is located opposite a toner carrying member (1), which includes a sleeve (1a) provided on the outer circumference of a magnet member (1b) having a plurality of magnetic poles (S 1 , N 1 , S 2 , N 2 ) on its surface, a recording electrode (3) in matrix form is located between the toner carrying member (1) and the background electrode (2), wherein toner is caused to jump out from the toner carrying member (1) and become attached to a recording medium (4) disposed between the recording and background electrodes (3, 2) in response to a voltage applied to the recording electrode (3), and wherein the toner supplied onto the toner carrying member (1) contains at least a fixing resin and a magnetic powder, characterised in that the toner has an apparent density of 0.5 g/cm 3 or more and an angle of repose of 45° or less, and that the magnetic flux density on the toner carrying member (1) is 0.06 T or more. A direct recording apparatus including a background electrode (2) located opposite a toner carrying member (1), which includes a sleeve (1a) provided on the outer circumference of a magnet member (1b) having a plurality of magnetic poles (S 1 , N 1 , S 2 , N 2 ) on its surface, a recording electrode (3) in matrix form located between the toner carrying member (1) and the background electrode (2), means for supplying toner onto the toner carrying member (1), the toner containing at least a fixing resin and a magnetic powder, means for applying a voltage to the recording electrode (3) to cause toner to jump out from the toner carrying member (1) and become attached to a recording medium (4) disposed between the recording and the background electrodes (3, 2), characterised in that the toner has an apparent density of 0.5 g/cm 3 or more and an angle of repose of 45° or less, and that the magnetic flux density on the toner carrying member (1) is 0.06 T or more. The method of claim 1 or the apparatus of claim 2, wherein a doctor blade (5) is located opposite the toner carrying member (1) to regulate the thickness of toner layer formed on the toner carrying member (1) to 5 to 100 µm. The method of claim 1 or 3 or the apparatus of claim 2 or 3, wherein the magnetic powder of the toner has an avenge particle size of 0.1 to 3 µm and a coercive force of 40 to 400 A/cm. The method of any one of claims 1, 3 and 4 or the apparatus of any one of claims 2 to 4, wherein the toner contains 10 to 60 wt.% of the magnetic powder. The method of any one of claims 1 and 3 to 5 or the apparatus of any one of claims 2 to 5, wherein an inorganic fine powder such as SiO 2 , Al 2 O 3 or TiO 2 or metallic salt of stearic acid such as zinc stearate or calcium stearate is added to the outer circumference of the toner particles.

Inventors: ASANAE MASUMI, NOGUCHI KOUJI, OCHIAI MASAHISA, ASANAE, MASUMI, NOGUCHI, KOUJI, OCHIAI, MASAHISA, ASANAE, MASUMI, C/O HITACHI METALS, LTD., NOGUCHI, KOUJI, C/O HITACHI METALS, LTD., OCHIAI, MASAHISA, C/O HITACHI METALS, LTD.
Applicants: ARRAY PRINTERS AB
Application year: 1994
Main classification: G03G9
IPC codes: G03G9, G03G15, B41J2